Demonstration model of hot air motor and heat pump



Dec. 10, 1968 H. SCHULZE 3,415,054

DEMONSTRATION MODEL OF HOT AIR MOTOR AND HEAT PUMP Filed March 21-, 1967 2 Sheets-Sheet 1 THERMOMETER OR ELECTRIC /HEATER, OR OJECT TO BE COOLED Fig.2

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INVENTOR Ho rald Scihulze ATTORNEYS, a

H. SCHULZE Dec. 10, 1968 DEMONSTRATION MODEL OF HOT AIR MOTOR AND HEAT PUMP Filed March 21, 1967 2 Sheets-Sheet 2 INVENTOR Harold Schulze ATTORN GL5.

United States Patent 14 Claims. 32]. 60-24) ABSTRACT OF THE DISCLOSURE To demonstrate the fundamental principles of hot air motors and heat pumps, a working piston and a displacer piston are slidably mounted within a transparent cylinder which is water cooled in one portion of the cylinder by means of a transparent water jacket therearound. The working piston and displacer piston are connected to a common crank drive at a displacement angle of approximately 90 from each other. A heating element (or material to be cooled) is inserted in one end of the cylinder adjacent to the displacer piston and entered into a heat exchange relationship with the gas in the cylinder. The center of the displacer piston is hollow to permit gas flow therethrough and is packed with a porous material such as copper wool and Teflon wool. The demonstration model can be operated either as a hot air motor or as a heat pump to visibly demonstrate the operating principles of these devices to students.

Background of the invention The present invention relates to a demonstration model of a hot air motor and/or heat pump for demonstrating to students the fundamental operating principles of these devices. Such demonstration models are known in which a working piston and a displacer piston are slidably mounted in a common cylinder and are mutually displaceably connected to a common crank drive. The object of the present invention is to provide improvements in this type of demonstration model to simplify its manufacture, improve its operation, and increase its effectiveness of demonstration.

Summary 0] the invention This invention relates to improvements in demonstration models of a hot air motor and/ or heat pump which includes a transparent cylinder, means for cooling at least a portion of the cylinder, at working piston slidably mounted within the cylinder, and a displacer piston slidably mounted within the cylinder between one end of the working piston and one end of the cylinder. In the preferred embodiment of the invention, these improvements include a central recess in the end of the displacer piston facing away from the working piston, into which recess a projection secured to the cylinder housing may be introduced for receiving an element entering into heat exchange with the contents of the cylinder. It is possible to introduce into this projection selectively, and readily interchangeably, an electrical heating element, a thermometer, or a specimen which is to be cooled or heated. Due to the engagement of these elements in the central recess of the displacer piston, favorable conditions of heat exchange are produced.

In the preferred embodiment of the invention, the gas flow through the hollow displacer piston is controlled in such a manner that compressed gas is passed from the compression side of the displacer piston toward the cylinder wall and flows from there along the cylinder wall into the chamber between the displacer piston and the working piston. This measure serves for improving the 3,415,054 Patented Dec. 10, 1968 heat exchange with respect to the enclosing cylinder wall, which is cooled by a liquid or a gaseous cooling medium.

Moreover, it is advantageous to connect the central recess of the displacer piston with an annular groove at the circumference of the piston by way of at least one radial groove. In this case, the displacer piston may expediently be hollow and may be filled with a porous packing. This porous packing may be advantageously provided in a multi-layered fashion, preferably coarsely permeable at the intake side from the compression chamber, and finely permeable at the other side of the piston. One layer of the porous packing, preferably the one which is finely permeable, may consist of synthetic wool made from Teflon or the like. Both the central recess of the displacer piston and the connecting chamber to the annular groove at the circumference of the piston may be provided with a porous packing so that the air flowing therethrough enters into heat exchange with this packing. A material having a high heat capacity, for example fine-wired copper wool, is suitable for this portion of the packing. When Teflon wool is used, it is advantageous. to place the Teflon Wool at the upper end of the central recess of the displacer piston. During operation as a heat pump, it is possible that air entering into the porous packing from above at temperatures below the freezing point will clog the packing with condensed ice. Synthetic wools such as Teflon or the like reduce the ice formation because the water vapor deposit is greatly reduced on Teflon.

Brief description of the drawings FIGURE 1 is a vertical cross-sectional view of the cylinder portion of one embodiment of the invention.

FIGURE 2 is a partial vertical cross-sectional view of the displacer piston shown in FIGURE 1.

FIGURE 3 is an enlarged side elevation view, partly in section, of the crank mechanism for the embodiment shown in FIGURE 1.

FIGURE 4 is an elevational view, partly in section, of the crank mechanism for the embodiment shown in FIGURE 1 and taken substantially along the plane defined by reference line 44 of FIGURE 3.

Desdription of the preferred embodiment Before describing the preferred embodiment in detail, the general principles of the invention will first be discussed. In the construction of the hollow displacer piston of this invention, it may be advantageous that the gas inlet and outlet thereof act as a heat exchanger which may be cooled by means of a cooling medium contained in a hollow displacer piston rod. The displacer piston may be made-at least in the part thereof which faces away from the working piston-as a hollow body from transparent material such as glass. It is additionally advantageous to dispose in the central recess of the displacer piston interchangeable flow guiding rings for improving the heat exchange with the element which is introduced through the cylinder wall. Such flow guiding rings may consist of cork, foam rubber, or the like and must be so dimensional with respect to the elements which are respectively inserted that the gas flow is guided past these elements at a high speed and closely adjacent thereto.

It is further expedient that the working piston rod be tiltably positioned with respect to the displaced piston rod, and that the working piston be sealed to the cylinder wall by means of an annular groove with an O-shaped annular sealing ring and, in the same annular groove, that a porous lubricating ring be provided on the side of the O-ring adjacent to the displacer piston rod. The displacer piston is also preferably sealed to the cylinder wall in the same manner as the working piston by means of an O-ring and a porous lubricating ring in a common annular groove.

Additionally, the bottom of the displacer piston facing the working piston may advantageously be so beveled that it is approximately parallel to the surface of the Working piston in its tilted position. It is further expedient that the tiltable working piston be sealed ofl, with respect to the displacer piston rod which passes therethrough, by means of a resilient sealing element in the shape of a cap-type joint or gasket whose point of attachment to the working piston is offset in the axial direction with respect to the displacer piston rod.

In accordance with another alternative construction which may be used, the working piston may have a circumferential groove containing a resilient seal which communicates by way of a connection bore with the chamber above the working piston so that the loosely inserted resilient seal will be pressed against the inner wall of the cylinder housing by compression of the gas in the chamber. The surface of the displacer piston may also engage or interlock with the projection which is attached to the end of the cylinder in the manner of an upper die and a matrix. In the preferred embodiment, the cylinder wall is made from glass and cooled by an enclosing and equally transparent cooling water jacket. The drive for the Working piston and the displacer piston is taken from a common crank drive in a manner known per se.

One embodiment of the present invention is schematically illustrated in the drawing. Referring to FIGURE 1, a cylinder 1 made from glass or plastic supports a displacer piston 2 and a working piston 3 which are slidably positioned within the cylinder with respect to one another. The working piston 3 is rigidly secured to a hollow piston rod 4 which, along with a displacer piston 5, is connected to the drive shaft of a drive gear 7 by means of a lower crank drive or mechanism (FIGURES 3 and 4).

The displacer piston rod 5 is rigidly attached to the end of displacer piston 2 in the center thereof and passes through a central opening in the working piston 33, the central opening in working piston 3 being sealed by a resilient gasket 13. The displacer piston rod 5 and working piston rod 4 are connected to the common crank drive approximately 90 out of phase with each other as shown in FIGURES 3 and 4. The common crank drive is 1'0- tated by a drive wheel 7 which, when rotated, causes the two pistons to reciprocate with the cylinder approximately 90 out of phase with each other. During this reciprocating movement, working piston 3 tilts slightly fro-m one side to the other due to the tilting of its piston rod 4 as the crank drive is revolved, but this slight tilting action does not break the gas seal between working piston 3 and the sides of cylinder wall 1.

The interior of displacer piston 2 is hollow to permit the flow of gas therethrough and is preferably packed with a porous material which will be described in detail later. Within the central opening 16 of displacer piston 2 a flow guiding ring 17 is positioned to produce a rapid flow of gas in the immediate vicinity of an elongated object 18 projecting into the interior of the cylinder 1 through an opening 20 in the end thereof. The elongated element 18 is sealed within the end 20 of the cylinder 1 by a gasket 19. Although the elongated element 18 is shown as a thermometer in FIGURE 1, an electrical heating element or an object to be cooled or heated can be inserted in its place.

The transparent cylinder 1 is enclosed by a transparent cooling jacket 8 for receiving a cooling fluid such as water or air. The area of the cylinder 1 which is to be cooled is defined by sealing rings 26 and 27 which communicate between the outer wall of cylinder 1 and the inner wall of cooling jacket 8. A cooling fluid such as water or air is introduced into the space between sealing rings 26 and 27 and extracted therefrom through ports 34 and 35 which extend through the side Walls of cooling jacket 8.

Before discussing the detailed construction of the displacer piston 2 and working piston 3, the general operation of the demonstration model will first be discussed by describing several modes of operation thereof. To operate the invention as a hot air motor, an electric heating element is placed into the interior of cylinder 1 in place of the thermometer 18. At the beginning of the cycle for the hot air motor, the gas in cylinder 1 is essentially below displacer piston 2 and is compressed by the upward stroke of working piston 3 while at the same time being cooled by water jacket 8. During the next stroke of the cycle, the compressed and cooled gas is moved upward by the downward motion of the displacer piston, and is then heated by the electric heating element. This expands the gas and drives the working piston 3 downward. The gas in the cylinder is then moved down again by the upward motion of the displacer piston. Thus the gas within the cylinder is periodically moved from the heated part of the cylinder into the cooled lower part of the cylinder and back again. In order to avoid unnecessary heat transfer from the top to the bottom of the cylinder, the gas is passed through porous material within the hollow interior of the displacer piston, being cooled on its way down by the transfer of heat to the porous material and being heated on its way up by the heat contained in the porous material.

If the heating element is removed from the upper part of the cylinder 1 and replaced by a thermometer, or an element to be cooled, and the same cycle as described above for the heat engine is followed, the device will operate as a refrigerator and cool the upper part of the cylinder to a temperature which is lower than that of the water cooled lower part of the cylinder. Under these conditions, if the direction of revolution of the drive gear is reversed, the device acts as a heat pump as follows: In the upper position of displacer piston 2, the working gas therebelow expands and extracts heat from the cooling Water. The expanded gas, heated to ambient temperature, is then moved upwardly by the downward motion of displacer piston 2 and compressed by the up ward motion of working piston 3, thus delivering heat to the cylinder Walls. At the end of this cycle, the compressed gas is moved down again by displacer piston 2. Under these operating conditions, the device acts as a heat pump, deriving heat from the cooling water and delivering this heat plus a quantity of heat corresponding to the expended mechanical work to the upper part of the cylinder to raise the upper part of the cylinder to a higher temperature.

Thus it can be seen that the demonstration model of this invention can be utilized to demonstrate the principles not only of hot air motors, but also of heat pumps and refrigerators in a highly eifective manner.

The working piston rod 4 is hollow and opens at one end into the interior of the cylinder through a bore 15 (FIGURE 1) and is fitted at the other end with a gas port 28 (FIGURE 4). The hollow piston rod 4 is closed oif by a plug 29 (FIGURE 3) under the port 28. If desired, a manometer can be coupled to the port 28 to measure the pressure within the cylinder during its operating cycle as a motor. When a manometer is not used, the port 28 is closed off to prevent the escape of air from the interior of the cylinder.

The displacer piston rod 5 is movable through a central opening in working piston 3, which central opening is sealed off by a resilient cap-type member 13 which is secured to working piston 3 by a clamp assembly 12. A ring 30 of porous material containing a lubricant is attached to piston rod 5 below working piston 3 to provide lubrication for the portion of the piston rod passing through sealing member 13.

The displacer piston rod 5 is rigidly attached to an end piece 31 which is attached in spaced relation to the lower end of displacer piston 2 by a plurality of circumferentially spaced bolts such as bolt 32. End piece 31 serves to define a radial gap at the bottom of displacer piston 2 to direct the flow of gas from the hollow interior 16 of displacer piston 2 to the periphery of the piston so that the gas will be directed against the water cooled walls of cylinder 1 for more effective cooling.

Working piston 3 has an annular groove 9 at the circumference thereof containing an O-shaped annular seal or gasket 10. Arranged above the O-shaped annular seal 10 on the side of the displacer piston 2 is a circular diskshaped felt ring or washer 11 which is impregnated with a lubricant. It is also expedient to cause the annular groove 9 to communicate-within the inserted rubberelastic O-shaped annular seal or gasket 10-with the chamber above the working piston 3 by means of an angular bore 31.

The central recess 16 disposed within displacer piston 2 may be partially sealed off by means of an inserted cork ring 17 so that the thermometer 18, which projects with its bulb into the central recess 16, is positioned in favorable heat exchange with the emerging gas flow. The thermometer 18 is positioned in an inset plug or stopper 19, which is inserted into a correspondingly shaped projection 20 of the cylinder 1. Another O-shaped annular seal or gasket 21 is provided as a seal between the displacer piston 2 and the cylinder 1 and rests in an annular groove 22 in the displacer piston 2. A felt ring 23 for receiving the lubricant supply is positioned at the side of the O-shaped annular seal 21 facing away from the Working piston 3.

Visible in the inner hollow chamber 16 of the displacer piston 2 is a finely porous layer 24 of Teflon wool which is followed by a coarsely porous layer 25 of copper Wool or the like. The copper Wool extends from the central inner chamber radially toward the circumferential surface of the displacer piston and reaches approximately to the outermost circumferential limit of the displacer piston 2. The porous layers 24 and 25 act as a heat exchanger for gas flowing through the hollow interior of displacer piston 2 as described above.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

What is claimed is:

1. In a demonstration model of a heat pump and/or hot gas motor including a transparent cylinder, means for cooling at least a portion of said cylinder, a Working piston slidably mounted within said cylinder, and a displacer piston slidably mounted within said cylinder between one end of said working piston and one end of said cylinder, the improvement comprising an inwardly projecting element from said one end of said cylinder interchangeably secured thereto, means on said one end of said cylinder and on the adjacent end of said displacer piston for receiving said element and positioning the element to enter into a heat exchange relationship with gas within said cylinder, said means being arranged to cause said gas to flow through the displacer piston in close surrounding relationship to said element for facilitating a good heat exchange between said gas and said element, said element being readily removable from said one end of the cylinder, and said means for receiving and positioning said element including a central recess in said adjacent end of said displacer piston for receiving said projecting element.

2. A demonstration model as defined in claim 1 wherein said inwardly projecting element is an electric heater.

3. A demonstration model as defined in claim 1 wherein said inwardly projecting element is transparent, hollow and includes a temperature sensing and indicating means therein.

4. A demonstration model as defined in claim 1 Wherein a coolable heat exchanger is provided in said displacer piston and gas flowing through said displacer piston passes over said heat exchanger and then along the Wall of the cylinder between the displacer piston and the working piston.

5. A demonstration model as defined in claim 1 where in said displacer piston is hollow to permit gas flow through the center thereof, and further comprising means at the end of said displacer piston adjacent to said working piston for directing said gas flow against the walls of said cylinder for cooling.

6. A demonstration model as defined in claim 5 wherein said means at the end of said displacer piston adjacent to said working piston comprises an end piece attached in spaced relation to the end of said displacer piston for directing the gas flow through the center thereof against the walls of said cylinder.

7. A demonstration model as defined in claim 1 wherein said displacer piston is made of transparent material at least in the portion thereof adjacent to the end of said cylinder.

8. A demonstration model as defined in claim 1 and further comprising a flow guiding ring in the central recess of said displacer piston for improving: the heat exchange relationship between said projecting element and the gas within said cylinder.

9. In a demonstration model of .a heat pump and/or hot air motor including a transparent cylinder, means for cooling at least a portion of said cylinder, a working piston slidably mounted within said cylinder, and a displacer piston slidably mounted within said cylinder between one end of said working piston and one end of said cylinder, the improvement comprising means on said one end of said cylinder and on the adjacent end of said displacer piston for receiving an element and positioning the element to enter into a heat exchange relationship with the gas within said cylinder, said element being an inwardly projecting member removably secured to said one end of the cylinder, and said means for receiving and positioning said element including a central opening in the adjacent end of said displacer piston for receiving said projecting memher, said displacer piston is hollow to permit gas flow through the center thereof and further including a packing of porous material Within the hollow center of said displacer piston, said packing of porous material varies in density from a relatively coarse packing at the end of the displacer piston adjacent to the working piston to a relatively fine packing at the other end of the displacer piston, at least a portion of said packing of porous material comprising a synthetic wool made from Teflon or the like.

10. A demonstration model, as defined in claim 9 wherein said packing of porous material further comprises a metallic Wool made from copper or the like and said packing of porous material acting as a heat exchanger for gas flowing therethrough.

11. In a demonstration model of a heat pump and/or hot air motor including a transparent cylinder, means for cooling at least a portion of said cylinder, a working piston slidably mounted within said cylinder, and a displacer piston slidably mounted within said cylinder between one end of said working piston and one end of said cylinder, the improvement comprising means on said one end of said cylinder and on the adjacent end of said displacer piston for receiving an element and positioning the element to enter into a heat exchange relationship with the gas Within said cylinder, said element being an inwardly projecting member removably secured to said one end of the cylinder, and said means for receiving and positioning said element including a central opening in the adjacent end of said displacer piston for receiving said projecting member, said displacer piston being rigidly attached to a central piston rod which passes through an opening in said working piston, said working piston being rigidly attached to a tiltable piston rod which is eccentrically positioned with respect to the displacer piston rod, said working piston having an annular groove in the outer surface thereof containing an O-shaped annular sealing element and an annular lubrication ring made of a porous material.

12. In a demonstration model of .a heat pump and/or hot air motor including a transparent cylinder, means for cooling at least a portion of said cylinder, a working piston slidably mounted within said cylinder, and a displacer piston slidably mounted within said cylinder between one end of said working piston and one end of said cylinder, the improvement comprising means on said one end of said cylinder and on the adjacent end of said displacer piston for receiving an element and positioning the element to enter into a heat exchange relationship with the gas within said cylinder, said element being an inwardly projecting member removably secured to said one end of the cylinder, and said means for receiving and positioning said element including a central opening in the adjacent end of said displacer piston for receiving said projecting member, said working piston is tiltable, and the end of said displacer piston adjacent to said working piston, is beveled so that its surface will be approximately parallel to said working piston in the tilted position thereof.

13. In a demonstration model of a heat pump and/or hot air motor including a transparent cylinder, means for cooling at least a portion of said cylinder, at working piston slidably mounted within said cylinder, and a displacer piston slidably mounted within said cylinder between one end of said working piston and one end of said cylinder, the improvement comprising means on said one end of said cylinder and on the adjacent end of said displacer piston for receiving an element and positioning the element to enter into a heat exchange relationship with the gas within said cylinder, said element being an inwardly projecting member removably secured to said one end of the cylinder, and said means for receiving and positioning said element including a central opening in the adjacent end of said displacer piston for receiving said projecting member, said displacer piston being rigidly attached to a central piston rod which passes through an opening in said working piston, said working piston being rigidly attached to a tiltable piston rod which is eccentrically positioned with respect to the displacer piston rod, and a flexible sealing element attached to said working piston for slidably receiving said displacer piston rod and for preventing gas from flowing through said working piston around said displacer piston rod.

14. A demonstration model as defined in claim 13 and further comprising a lubrication ring made of a porous material encircling said displacer piston rod below said Working piston.

References Cited UNITED STATES PATENTS 309,163 12/1884 Robinson 60-24 1,042,560 10/1912 Kessler 6()24 2,726,482 12/1955 Roehrl et al 13 X 2,797,971 7/1957 Greenough 277-176 3,117,414 1/1964 Daniels et al -24 3,218,815 11/1965 Chellis et al. 62-6 EDGAR W. GEOGHEGAN, Primary Examiner.

CARROLL B. DORITY, Assistant Examiner.

US. Cl. X.R. 626; 33-13 

